The present invention relates in general to an assisted breathing device or medical ventilator that may be used in a variety of human and animal patient applications, such as, but not limited to, medical facilities (e.g., hospitals, physiciansxe2x80x2 and veterinary offices and the like), as well as medical field unit and emergency vehicle applications. The invention is particularly directed to a new and improved portable medical ventilator that provides both precision pneumatic regulation of tidal/forced breathing, and continuous positive airway pressure (CPAP)-based spontaneous breathing capability.
Currently available portable medical ventilator units generally fall into one of two categories: i- relatively simple or limited capability pneumatically controlled units (typically carried by emergency vehicles), and ii-sophisticated electrically (both AC and battery) powered, electronically (microprocessor)-controlled systems, that are essentially comparable in function to in-house (e.g., hospital) devices. The former devices suffer from the fact that they are not much more that emergency oxygen supplies. An obvious drawback to the devices of the second category is the fact that, as electrically powered, system level pieces of equipment, they are relatively expensive and complex. Moreover, electronic systems are subject to a number of adverse influences, such as electromagnetic interference, handling abuse, and battery life-factors which do not affect a pneumatic system.
In accordance with the present invention, drawbacks of conventional medical ventilator devices such as those described above are effectively obviated by a new and improved portable, pneumatically controlled medical ventilator that provides the multiple functionality of an electronically controlled ventilator, but without the need for any electrical power (including batteries), thereby making the unit especially suited for field and emergency vehicle applications.
For this purpose, the pneumatically controlled medical ventilator of the present invention has an input port coupled to a source of pressurized gas, such as an oxygen tank carried by a medical emergency vehicle. A pneumatic link from the input port is coupled to a system-priming gas flow control switch, which is operative to prime a pneumatic timing cartridge within a pneumatic timing unit, when the ventilator is initially coupled to the oxygen source. The input port is further coupled to a system gas flow pressure regulator. The output of the system gas flow pressure regulator is coupled to an input port of a tidal breathing control switch, the operation of which controls the flow of mandatory tidal breathing gas to the patient.
The system gas flow pressure regulator provides a prescribed elevated or positive driving pressure for the mandatory tidal breathing gas supply subsystem, so that a precisely regulated amount of breathing gas may be controllably supplied to the patient. This constant positive pressure is considerably higher than the nominal lung pressure of a patient, so that it is effective to prevent collapse of the patient""s lungs, and is not affected by changes in the patient""s lung compliance and resistance.
The filtered breathing gas supplied is further coupled to a continuous positive airway pressure (CPAP) valve. The CPAP valve has a sensing or control port coupled to the breathing gas supply throat of a patient air supply output coupler for sensing a drop in pressure when the patient initiates or demands a breath, separate from a mandatory tidal breathing cycle. A section of breathing gas supply tubing is coupled between the patient air supply output coupler and an airway breathing interface on the patient. In response to the patient spontaneously drawing a breath, the drop in pressure in the breathing gas supply throat of the output coupler will cause the CPAP valve to couple the breathing gas (oxygen) to a gated venturi unit installed at an upstream end of the patient air supply output coupler. The venturi unit includes an ambient air input port through which filtered ambient air is drawn into the patient air supply output coupler by the flow of pressurized oxygen supplied to input port, and thereby allow a prescribed spontaneous or on-demand oxygen-enriched breathing mixture to be supplied to the patient.
An auxiliary anti-suffocation valve is coupled to the main airflow passageway of the patient air supply output coupler, to ensure that ambient air can be drawn into the main airflow passageway and supplied to the patient, in the event of a ventilator failure or depressurization of the oxygen source. Also, an overpressure valve is coupled to the main airflow passageway of the patient air supply output coupler, to prevent an excess pressure build up within the main airflow passageway of the coupler, and within the patient""s lungs.
The presetable gas pressure provided at the output port of the CPAP valve is further coupled to a pneumatic conduit for inflating the diaphragm of an exhalation valve of an airway breathing interface on the patient. When a breath drawn in by the patient is patient-initiated, the pressured gas supplied by CPAP valve to the exhalation valve outlet inflates the exhalation valve""s diaphragm and prevents the breathing gas in the tubing breathing gas tubing from being exhausted from the exhalation valve, and instead directed into the patient""s airway, as intended. When the patient ceases inhaling, there is no longer a pressure drop in the coupler throat, causing the CPAP valve to close, and interrupt the positive pressure at the exhalation valve outlet. The exhalation valve""s diaphragm thereby deflates to allow the patient to exhale.
The pneumatic timing unit supplies a periodic pneumatic control signal associated with a controllable (oxygen) concentration and rate of tidal breathing gas to a normally closed tidal breathing control switch. Tidal breathing parameters of the pneumatic control signal supplied to the pneumatic timing unit includes a pneumatic timing cartridge and a pneumatic time constant circuit for controlling the charge and bleed rates of the pressurized gas. The tidal breathing control switch receives the pressure-regulated oxygen from the system pressure regulator, and outputs a pressure-regulated oxygen to a dual position tidal air supply-mixture switch.
For a first position, the tidal air supply-mixture switch couples the pressure-regulated oxygen from the tidal breathing pneumatic circuitry to an oxygen concentration-reducing venturi, that is coupled to the output throat of the patient air supply coupler. To supply a pure (100%) oxygen breathing gas to the patient""s airway breathing interface, the tidal air supply-mixture switch is turned, and thereby ported to a 100% oxygen outlet port, which is coupled through a section of oxygen supply tubing to a pure oxygen feed input port of the patient""s airway breathing interface.
A manually setable, pressure regulator valve is coupled to the tidal breathing supply, and is operative to feed the exhalation valve outlet. As with the operation of the CPAP valve for an on-demand breath, this serves to inflate the exhalation valve""s diaphragm, and prevent the breathing gas from being exhausted from the exhalation valve, but directed instead into the patient""s airway. At the end of the tidal breath interval, the positive pressure at the output of the tidal breathing control switch is interrupted, terminating the positive pressure at the output of the pressure limit regulator valve necessary for inflating the diaphragm of the exhalation valve. The exhalation valves diaphragm deflates to allow the patient to exhale.